Fuel cell system

ABSTRACT

The invention provides a reactant delivery system for a dead-headed PEM fuel cell system, comprising a fuel cell, a fuel supply, a purge valve, an inlet orifice, an outlet orifice, and a controller. A first fuel flow circuit is provided, wherein fuel is flowed from the fuel supply to the inlet orifice, through the fuel cell from the inlet orifice, and through the outlet orifice from the fuel cell to the purge valve. A second fuel flow circuit is also provided, wherein fuel is flowed from the fuel supply to the outlet orifice, through the fuel cell from the outlet orifice, and through the inlet orifice from the fuel cell to the purge valve. A valve means is coupled to the controller and adapted to transfer fuel flow between the first flow circuit and the second flow circuit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/232,293, entitled “FUEL CELL SYSTEM,” filed on Aug. 30, 2002; whichclaims priority under 35 USC 119(e) from U.S. Provisional ApplicationNo. 60/316,499, entitled “FUEL CELL SYSTEM,” filed Aug. 31, 2001.

BACKGROUND

The invention generally relates to a fuel cell system that providesimproved performance and an increased system lifetime.

A fuel cell is an electrochemical device that converts chemical energyproduced by a reaction directly into electrical energy. For example, onetype of fuel cell includes a polymer electrolyte membrane (PEM), oftencalled a proton exchange membrane, that permits only protons to passbetween an anode and a cathode of the fuel cell. At the anode, diatomichydrogen (a fuel) is reacted to produce protons that pass through thePEM. The electrons produced by this reaction travel through circuitrythat is external to the fuel cell to form an electrical current. At thecathode, oxygen is reduced and reacts with the protons to form water.The anodic and cathodic reactions are described by the followingequations:H₂→2H⁺+2e ⁻  (1) at the anode of the cell, andO₂+4H⁺+4e ⁻→2H₂O  (2) at the cathode of the cell.

A typical fuel cell has a terminal voltage of up to about one volt DC.For purposes of producing much larger voltages, multiple fuel cells maybe assembled together to form an arrangement called a fuel cell stack,an arrangement in which the fuel cells are electrically coupled togetherin series to form a larger DC voltage (a voltage near 100 volts DC, forexample) and to provide more power.

The fuel cell stack may include flow field plates (graphite composite ormetal plates, as examples) that are stacked one on top of the other. Theplates may include various surface flow field channels and orifices to,as examples, route the reactants and products through the fuel cellstack. The flow field plates are generally molded, stamped or machinedfrom materials including carbon composites, plastics and metal alloys. APEM is sandwiched between each anode and cathode flow field plate.Electrically conductive gas diffusion layers (GDLs) may be located oneach side of each PEM to act as a gas diffusion media and in some casesto provide a support for the fuel cell catalysts. In this manner,reactant gases from each side of the PEM may pass along the flow fieldchannels and diffuse through the GDLs to reach the PEM. The GDL'sgenerally comprise either a paper or cloth based on carbon fibers. ThePEM and its adjacent pair of catalyst layers are often referred to as amembrane electrode assembly (MEA). An MEA sandwiched by adjacent GDLlayers is often referred to as a membrane electrode unit (MEU), or alsoas an MEA. Common membrane materials include Nafion™, Gore Select™,sulphonated fluorocarbon polymers, and other materials such aspolybenzimidazole and polyether ether ketone. Various suitable catalystformulations are also known in the art, and are generallyplatinum-based.

A fuel cell system may include a fuel processor that converts ahydrocarbon (natural gas or propane, as examples) into a fuel flow forthe fuel cell stack. For a given output power of the fuel cell stack,the fuel flow to the stack must satisfy the appropriate stoichiometricratios governed by the equations listed above. Thus, a controller of thefuel cell system may monitor the output power of the stack and based onthe monitored output power, estimate the fuel flow to satisfy theappropriate stoichiometric ratios. In this manner, the controllerregulates the fuel processor to produce this flow, and in response tothe controller detecting a change in the output power, the controllerestimates a new rate of fuel flow and controls the fuel processoraccordingly.

The fuel cell system may provide power to a load, such as a load that isformed from residential appliances and electrical devices that may beselectively turned on and off to vary the power that is demanded by theload. Thus, the load may not be constant, but rather the power that isconsumed by the load may vary over time and abruptly change in steps.For example, if the fuel cell system provides power to a house,different appliances/electrical devices of the house may be turned onand off at different times to cause the load to vary in a stepwisefashion over time. Fuel cell systems adapted to accommodate variableloads are sometimes referred to as “load following” systems.

There is a continuing need for design improvements to improve theefficiency and performance of such systems.

SUMMARY

The invention provides a reactant delivery system and associated methodsof operation for dead-headed PEM fuel cell systems. In one aspect, theinvention provides a reactant delivery system wherein a fuel cell has afirst orifice and a second orifice. The first and second orifices are influid communication such that a reactant can pass between them throughthe fuel cell. A fuel supply, such as a pressure vessel or conduitcontaining hydrogen, is coupled to the first orifice along a firstconduit. The first conduit has a first valve adapted to regulate flowbetween the first conduit and the fuel cell. The first conduit iscoupled to a second conduit at a location between the fuel supply andthe first valve. The first conduit is coupled to a third conduit at alocation between the first valve and the fuel cell. A purge valve iscoupled to the second orifice along a fourth conduit. The fourth conduithas a fourth valve adapted to regulate flow between the fourth conduitand the fuel cell. The fourth conduit is coupled to the second conduitat a location between the fuel cell and the fourth valve. The fourthconduit is coupled to the third conduit at a location between the fourthvalve and the purge valve. The second conduit has a second valve adaptedto regulate flow between the first conduit and the fourth conduit. Thethird conduit has a third valve adapted to regulate flow between thefirst conduit and the fourth conduit.

Systems under the present invention can include various additionalfeatures as discussed herein, either alone or in combination. In someembodiments, the second conduit can further include a first check valveadapted to prevent flow from the fourth conduit to the first conduit.Similarly, the third conduit can further include a second check valveadapted to prevent flow from the fourth conduit to the first conduit.

In some embodiments, the system can further include a controller coupledto the first, second, third and fourth valves. As an example, thecontroller can have a first mode of operation wherein the controlleropens the first and fourth valves and closes the second and thirdvalves. In a second mode of operation, the controller closes the firstand fourth valves and opens the second and third valves. The system thusreverses the direction of reactant flow through the fuel cell.

The controller can be adapted to alternate between the first and secondoperating modes at successive time intervals of a predetermined size. Asan example, the controller can be adapted to monitor a performanceparameter of the fuel cell, and be configured to alternate between thefirst and second operating modes (e.g., reverse reactant flow) when theperformance parameter falls below a predetermined level. As an example,in some embodiments, the performance parameter can be a voltage of thefuel cell, such that the controller alternate between the first andsecond operating modes when the voltage falls below 0.4 volts.

In some embodiments, the system may include a third mode of operationwherein the controller is adapted to open the purge valve for apredetermined period of time (e.g., to purge inert componentsaccumulated in the anode chamber of the fuel cell as it is operated indead-headed mode). As an example, the controller can be adapted tooperate in the third operating mode as an intermediate step toalternating between the first and second operating modes.

In another aspect, the invention provides a reactant delivery system fora dead-headed PEM fuel cell system, comprising a fuel cell, a fuelsupply, a purge valve, an inlet orifice, an outlet orifice, and acontroller. A first fuel flow circuit is provided, wherein fuel isflowed from the fuel supply to the inlet orifice, through the fuel cellfrom the inlet orifice, and through the outlet orifice from the fuelcell to the purge valve. A second fuel flow circuit is also provided,wherein fuel is flowed from the fuel supply to the outlet orifice,through the fuel cell from the outlet orifice, and through the inletorifice from the fuel cell to the purge valve. A valve means is coupledto the controller and adapted to transfer fuel flow between the firstflow circuit and the second flow circuit.

In some embodiments, the valve means comprises a first valve, a secondvalve, a third valve and a fourth valve, wherein the first valveregulates flow from the fuel supply to the first flow circuit, whereinthe second valve regulates flow from the fuel supply to the second flowcircuit, wherein the third valve regulates flow from the second circuitto the purge valve, and wherein the fourth valve regulates flow from thefirst circuit to the purge valve.

In some embodiments, the second flow circuit intersects the first flowcircuit at a location on the first flow circuit between the fourth valveand the purge valve. A first check valve is provided in the secondcircuit at a location between the third valve and the intersection ofthe first and second flow circuits, the first check valve being adaptedto prevent flow from the first flow circuit to the third valve. A secondcheck valve is provided in the first circuit at a location between thesecond valve and the intersection of the first and second flow circuits,the second check valve being adapted to prevent flow from the secondflow circuit to the second valve.

In some embodiments, the valve means comprises a first three-way valvehaving a first position directing flow from the fuel supply to the firstcircuit, and a second position directing flow from the fuel supply tothe second circuit. Other valve arrangements are possible.

In another aspect, the invention provides a method of operating a fuelcell system, including at least the following steps: (1) coupling ahydrogen supply to an inlet of a dead-headed fuel cell; (2) pressurizingthe fuel cell inlet with hydrogen from the hydrogen supply; (3) reactingat least a portion of the hydrogen in the fuel cell to supply electricalcurrent to a load; (4) opening an outlet of the fuel cell to allowhydrogen to flow through the fuel cell; (5) removing the hydrogen supplyfrom the inlet of the fuel cell and closing the inlet of the fuel cell;(6) coupling the hydrogen supply to the outlet of the fuel cell; (7)pressurizing the fuel cell outlet with hydrogen from the hydrogensupply; (8) reacting at least a portion of the hydrogen in the fuel cellto supply electrical current to the load; and (9) opening the inlet ofthe fuel cell to allow hydrogen to flow through the fuel cell.

In some embodiments, an additional step may include alternating atsuccessive time intervals of a predetermined size the steps of couplingthe hydrogen supply to the inlet of the fuel cell and coupling thehydrogen supply to the inlet of the fuel cell. For example, the systemcan be configured to periodically purge itself and reverse thedirections that hydrogen is fed to the fuel cell.

Various embodiments may include the additional steps: (1) monitoring aperformance parameter of the fuel cell; and (2) performing the step ofcoupling the hydrogen supply to the outlet of the fuel cell when theperformance parameter falls below a predetermined level.

In some embodiments, the purging steps can each include purging the fuelcell for a predetermined period of time. As an additional feature,methods under the invention may include: (1) coupling a battery to theload to supply power to the load during the step of opening an outlet ofthe fuel cell; and (2) coupling the battery to the load to supply powerto the load during the step of opening the inlet of the fuel cell.

In another aspect, the invention provides a method of operating a fuelcell system, including the following steps: (1) pressurizing adead-headed fuel cell with hydrogen by coupling a first orifice of thefuel cell to a hydrogen supply, the fuel cell having a second orifice ina closed position; (2) reacting at least a portion of the hydrogen inthe fuel cell to supply electrical current to a load; (3) closing thefirst orifice and opening the second orifice; (4) pressurizing the fuelcell with hydrogen by coupling the second orifice of the fuel cell tothe hydrogen supply; and (5) reacting at least a portion of the hydrogenin the fuel cell to supply electrical current to the load. Someembodiments may include purging the fuel cell prior to the step ofpressurizing the fuel cell.

In another aspect, the invention provides a method of operating a fuelcell system, including the following steps: (1) dead-heading an anodechamber of a fuel cell; (2) flowing hydrogen into a first orifice of theanode chamber; (3) reacting at least a portion of the hydrogen in theanode chamber to supply electrical current to a load; (4) flowinghydrogen into a second orifice of the anode chamber; and (5) reacting atleast a portion of the hydrogen in the anode chamber to supplyelectrical current to the load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a fuel cell.

FIG. 2 is a block diagram of an embodiment of a system including a fuelcell.

FIG. 3 is a block diagram of an embodiment of a system including a fuelcell.

FIG. 4 is a schematic diagram of an embodiment of a dead headed fuelcell system.

DETAILED DESCRIPTION

A simplified fuel cell system is contemplated which utilizes asubstantially pure anode reactant (hydrogen) and either air or asubstantially pure cathode reactant (oxygen). In some cases the stack ofsuch a fuel cell system may be “dead headed” to contain all of thehydrogen (and/or the oxidant) within the stack until a sufficient amounthas been reacted. Periodically the dead headed stack may be vented orpurged. Hydrogen and/or oxidant that have not been reacted in the fuelcell stack may be vented to the atmosphere or re-circulated through thestack (purged), and in some cases may be oxidized before it is vented.In a dead headed system a tank may be provided which contains dry orsub-saturated hydrogen for use within the fuel cell assembly. Suchsub-saturated reactants may dry out the leading edge of the membrane andin turn lead to premature membrane decay.

Operation of a dead headed hydrogen fuel cell has typically occurred asfollows: Hydrogen is input to the stack at the anode inlet. The anodeoutlet is dead-ended with a purge valve. During operation, hydrogenenters the anode side of the fuel cell, passes through the membrane asload is applied, and reacts with oxygen on the cathode side, formingwater. Some amount of water may back diffuse from the cathode side tothe anode side. Nitrogen may also diffuse to the anode side. Factorssuch as the increased amount of nitrogen and water diffusion eventuallycause cell performance to drop, and when this occurs a purge valve istriggered to open and close.

FIG. 1 shows an embodiment of a PEM fuel cell 10 including flow fieldplates 20 and 30, a PEM 40, catalysts 50 and 60 and gas diffusion layers70 and 80. It will be appreciated by those skilled in the art that theinvention can be practiced with a single fuel cell or a plurality offuel cells arranged in a fuel cell stack.

FIG. 2 shows a system 205 including flow field plate 20 of fuel cell 10.Flow field plate 20 has regions 100 and 110, and open faced channels 120that define a flow path for reactant gas (e.g., oxidant gas, such as airor oxygen, or fuel gas, such as hydrogen or hydrocarbon) between regions100 and 110. Flow field plate 20 is fluidly connected to a reactant gassource 130, devices (e.g., valves) 140, 150 and 160, and tubes 170, 180,190, 200, 210, 220 and 230. Each of devices 140, 150 and 160 has atleast two positions which allow a gas to flow through system 205 alongdifferent paths so that system 205 has at least two operational states.

In one operational state, devices 140, 150 and 160 are positioned sothat the reactant gas flows from source 130 to region 100 along tubes170, 180 and 190. The gas flows from region 100 to region 110 viachannels 120. The gas exits flow field plate 20 at region 110 alongtubes 220 and 230. In this operational state, gas does not flow frombetween tubes 190 and 200, since valve 150 diverts flow from tube 180 totube 190. Valve 140 is configured such that gas also does not flowbetween tubes 210 and 170. Valve 160 is configured such that gas doesnot flow between tubes 210 and 220, or between tubes 210 and 230.

In a different operational state, devices 140, 150 and 160 areconfigured so that the reactant gas flows from source 130 to region 110(instead of region 100 in the first operational state) along tubes 170,210 and 230. The gas flows from region 110 to region 100 via channels120. The gas exits flow field plate 20 at region 100 along tubes 190 and200. In this operational state, gas does not flow from between tubes 220and 230. Gas also does not flow between tubes 180 and 170, between tubes180 and 190, or between tubes 180 and 200.

Switching the operational state of system 205 has the effect ofreversing the flow of the reactant gas through flow field plate 20. Theoperational state can be switched during the purge cycle of fuel cellsystem operation. Generally, the operational state is switched whilereactant gas is not flowing through flow field plate 20. In one example,reactant gas can flow through flow field plate 20 (e.g., so that thefuel cell produces a non-zero power output) for a desired period oftime. The flow of reactant gas is then stopped (e.g., so that the fuelcell produces a power output of about zero), and the operational stateof system 205 is changed. The desired period of time can be based, forexample, on a purge cycle of the fuel cell, which can be measuredmanually and/or automatically. In general, the operational state ofsystem 205 can be switched manually and/or automatically.

FIG. 3 shows a system 208 designed so that its operational states can beautomatically switched. System 208 includes a monitor 310 that measuresone or more performance characteristics of system 208. Such performancecharacteristics are known to those skilled in the art and include, forexample, power output, voltage or the amount of the time that the fuelcell has been operating. Other performance characteristics may also bemonitored. When the measured parameter(s) fall below some predeterminedvalue (e.g., a cell voltage falls below 0.4 volts), monitor 310 sends asignal to a controller 320. Controller 320 begins a purge cycle of fuelcell system 208 by changing the positions of devices 140, 150 and 160.This changes the operational state of fuel cell 10 by reversing the flowof gas through flow field plate 20. This evacuates the fuel cell stackof residual reactant gases and inerts. Typically, controller 320 stopsthe flow of gas through flow field plate (e.g., by closing device 140)so that the power output of fuel cell 10 drops to zero. Then, controller320 switches the positions of devices 140, 150 and 160 to reverse gasflow through flow field plate 20.

System 208 can also be designed so that the operational state of system208 is manually changed. For example, monitor 310 can be designed toprovide a read-out that can be read by a maintenance technician.Depending upon the read-out of monitor 310, the technician can manuallychange the positions of devices 140, 150 and 160 to change theoperational state of system 208. In some embodiments, system 208 isdesigned so that the operational state of system 208 can be changed bothmanually and automatically.

In other embodiments, the operational state of systems 205 and 208 canbe reversed as follows. Devices 140, 150 and 160 are positioned so thatgas does not flow through the system (e.g., devices 140, 150 and 160 areclosed). Tubes 190 and 230 are disconnected from devices 150 and 160,respectively. Flow field plate 20 is then rotated (e.g., rotated 180°),and tubes 190 and 230 are connected to devices 160 and 150,respectively. Typically, rotating flow field plate 20 involves rotatingfuel cell 10. In certain embodiments, however, flow field plate 20 canbe rotated without rotating other components of fuel cell 10.

FIG. 4 illustrates, in schematic format, a dead headed hydrogen fuelcell system 400 having the ability to periodically alternate thedirection of reactant flows through fuel cell stack 412. For simplicity,the oxidant gas circuit of system 400 is not shown. In normal operatingmode the certain indicated valves are opened while others remain closed.When it is determined that the fuel cell system requires a purging ofthe reactants, the alternated valve conditions are triggered. Thisreverses flow of the reactant gases while simultaneously conducting apurge.

The operational states of the system of FIG. 4 are summarized in Table1: TABLE I State B (NFV-1 & NFV-2 Open) State A (NFV-1 & NFV-2 Closed)401 - ALTV-1 CLOSED 401 - ALTV-1 OPEN 402 - NFV-1 OPEN 402 - NFV-1CLOSED 403 - ALTV-2 CLOSED 403 - ALTV-2 OPEN 404 - ALTCV-1 CV BLOCKING404 - ALTCV-1 CV FLOWING 405 - NFV-2 OPEN 405 - NFV-2 CLOSED 406 -ALTCV-2 CV BLOCKING 406 - ALTCV-2 CV FLOWING 407 - P1 INLET PRESSURE407 - P1 OUTLET PRESSURE 408 - T1 INLET TEMPERATURE 408 - T1 OUTLETTEMPERATURE 409 - P1 OUTLET PRESSURE 409 - P1 INLET PRESSURE 410 - T1OUTLET 410 - T1 INLET TEMPERATURE TEMPERATURE

The direction of flow through fuel cell stack 412 in state A isindicated by inlet arrow 414 and outlet arrow 416. The direction of flowthrough fuel cell stack 412 in state B is indicated by inlet flowdirection arrow 418 and outlet flow direction arrow 420. The fuel gasenters the system 400 through conduit 422 (e.g., connected to a pressureregulator on a hydrogen tank). As an example, in operating state B,valves 401 and 403 are closed and valve 402 is open, such that the fuelgas enters fuel cell stack 412 as indicated by arrow 418. Temperatureand pressure indicators 407 and 408 measure the inlet temperature andpressure conditions. While valve 405 is open in this state, the systemis dead-headed since a purge valve (not shown) on outlet conduit 424 isclosed. Temperature and pressure indicators 409 and 410 measure thetemperature and pressure conditions at the outlet of fuel cell stack412.

When the system is switched to operating state A, as indicated in Table1, valve 402 is closed and valve 401 is opened, such that the fuel gasflows through one-way valve 404 and into stack 412 as shown by flowdirection arrows 414 and 416. In this mode, valve 403 is opened to allowthe gas to be purged through one-way valve 406 when the purge valve onconduit 424 is opened. Valve 405 is closed to avoid back flow into fuelcell 412.

In alternate terms, the system 400 shown in FIG. 4 can be described as areactant delivery system wherein a fuel cell has a first orifice 426 anda second orifice 428. The first and second orifices 426, 428 are influid communication such that a reactant can pass between them throughthe fuel cell 412. A fuel supply 422, such as a pressure vessel orconduit containing hydrogen, is coupled to the first orifice 426 along afirst conduit 430. The first conduit 430 has a first valve 402 adaptedto regulate flow between the first conduit 430 and the fuel cell 412.The first conduit 430 is coupled to a second conduit 432 at a location434 between the fuel supply 422 and the first valve 402. The firstconduit 430 is coupled to a third conduit 435 at a location 436 betweenthe first valve 402 and the fuel cell 412. A purge valve 424 is coupledto the second orifice 428 along a fourth conduit 438. The fourth conduit438 has a fourth valve 405 adapted to regulate flow between the fourthconduit 438 and the fuel cell 412. The fourth conduit 438 is coupled tothe second conduit 432 at a location 442 between the fuel cell 412 andthe fourth valve 405. The fourth conduit 438 is coupled to the thirdconduit 435 at a location 440 between the fourth valve 405 and the purgevalve 424. The second conduit 432 has a second valve 401 adapted toregulate flow between the first conduit 430 and the fourth conduit 438.The third 435 conduit has a third valve 403 adapted to regulate flowbetween the first conduit 430 and the fourth conduit 438.

The operation of such systems may also be described as a method. Forexample, such a method could include the following steps: (1) coupling ahydrogen supply 422 to an inlet 426 of a dead-headed fuel cell 412; (2)pressurizing the fuel cell inlet 426 with hydrogen from the hydrogensupply 422; (3) reacting at least a portion of the hydrogen in the fuelcell 412 to supply electrical current to a load (not shown); (4) openingan outlet 428 of the fuel cell 412 to allow hydrogen to flow through thefuel cell 412; (5) removing the hydrogen supply 422 from the inlet 426of the fuel cell 412 and closing the inlet 426 of the fuel cell 412; (6)coupling the hydrogen supply 422 to the outlet 428 of the fuel cell 412;(7) pressurizing the fuel cell outlet 428 with hydrogen from thehydrogen supply 422; (8) reacting at least a portion of the hydrogen inthe fuel cell 412 to supply electrical current to the load; and (9)opening the inlet 426 of the fuel cell to allow hydrogen to flow throughthe fuel cell 412. Methods of operation may also be described in otherways, foe example as set forth in the claims, and may include any of thedesign aspects, features or additional steps discussed herein, eitheralone or in combination.

As an additional feature of systems such as discussed with respect toFIG. 4, a coolant flow circuit (not shown) can be arranged so that theflow of coolant is concurrent with or counter to the flow of one or moreof the reactant gases in the fuel cell. Typically, the flow of coolantis concurrent with the flow of the reactant gases. In some embodiments,the flow of coolant is stopped and reversed during the period of timethat the flow of reactant gas is stopped and reversed. Thus, the flow ofreactant gas can be reversed without switching the direction of coolantflow relative to the flow direction of the reactant gas.

Furthermore, those skilled in the art will appreciate that devices, suchas one or more batteries, can be connected to the fuel cell or fuel cellstack so that, during the time period that the power output of the fuelcell or fuel cell stack is about zero (e.g., when reactant gas flow isstopped), power output from the battery can be used in place of the fuelcell.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art, having the benefit of thisdisclosure will appreciate numerous modifications and variationstherefrom. It is intended that the invention covers all suchmodifications and variations as fall within the true spirit and scope ofthe invention.

1. A method of operating a fuel cell system, comprising: coupling ahydrogen supply to an inlet of a dead-headed fuel cell; pressurizing thefuel cell inlet with hydrogen from the hydrogen supply; reacting atleast a portion of the hydrogen in the fuel cell to supply electricalcurrent to a load; opening an outlet of the fuel cell to allow hydrogento flow through the fuel cell; removing the hydrogen supply from theinlet of the fuel cell and closing the inlet of the fuel cell; couplingthe hydrogen supply to the outlet of the fuel cell; pressurizing thefuel cell outlet with hydrogen from the hydrogen supply; reacting atleast a portion of the hydrogen in the fuel cell to supply electricalcurrent to the load; and opening the inlet of the fuel cell to allowhydrogen to flow through the fuel cell.
 2. The method of claim 1,further comprising: alternating at successive time intervals of apredetermined size the steps of coupling the hydrogen supply to theinlet of the fuel cell and coupling the hydrogen supply to the inlet ofthe fuel cell.
 3. The method of claim 1, further comprising: monitoringa performance parameter of the fuel cell; and performing the step ofcoupling the hydrogen supply to the outlet of the fuel cell when theperformance parameter falls below a predetermined level.
 4. The methodof claim 1, wherein the performance parameter is a voltage of the fuelcell, and the predetermined threshold is 0.4 volts.
 5. The method ofclaim 1, wherein the step of opening an outlet of the fuel cell includespurging the fuel cell for a predetermined period of time, and whereinthe step of opening the inlet of the fuel cell includes purging the fuelcell for a predetermined period of time.
 6. The method of claim 1,further comprising: coupling a battery to the load to supply power tothe load during the step of opening an outlet of the fuel cell; andcoupling the battery to the load to supply power to the load during thestep of opening the inlet of the fuel cell.
 7. A method of operating afuel cell system, comprising: pressurizing a dead-headed fuel cell withhydrogen by coupling a first orifice of the fuel cell to a hydrogensupply, the fuel cell having a second orifice in a closed position;reacting at least a portion of the hydrogen in the fuel cell to supplyelectrical current to a load; closing the first orifice and opening thesecond orifice; pressurizing the fuel cell with hydrogen by coupling thesecond orifice of the fuel cell to the hydrogen supply; and reacting atleast a portion of the hydrogen in the fuel cell to supply electricalcurrent to the load.
 8. The method of claim 7, further comprising:purging the fuel cell prior to the step of pressurizing the fuel cell.9. The method of claim 8, further comprising: monitoring a performanceparameter of the fuel cell; and performing the step of purging the fuelcell when the performance parameter falls below a predetermined level.10. A method of operating a fuel cell system, comprising: dead-headingan anode chamber of a fuel cell; flowing hydrogen into a first orificeof the anode chamber; reacting at least a portion of the hydrogen in theanode chamber to supply electrical current to a load; flowing hydrogeninto a second orifice of the anode chamber; and reacting at least aportion of the hydrogen in the anode chamber to supply electricalcurrent to the load.
 11. The method of claim 10, further comprising:purging the fuel cell prior to the step of flowing hydrogen into asecond orifice of the anode chamber.
 12. The method of claim 11, furthercomprising: monitoring a performance parameter of the fuel cell; andperforming the step of purging the fuel cell when the performanceparameter falls below a predetermined level.